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Engine startup experiments with intake port sampling were performed in a modified fuel injected single cylinder gasoline CFR research engine. Immediately after fuel injection, port fuel-air vapor sampling was performed in order to quantify the role of the fuel injector in creating a combustible mixture for the first cycle of engine startup. In-cylinder sampling was also performed to clarify the role of other mixture preparation mechanisms in the startup process. Sample analysis was performed using gas chromatography. Experimental data were also collected during steady-state operating conditions at the same intake port pressure and temperature as that of the first cranking cycle for comparison. Results show that approximately ½ to ¾ of a near stoichiometric combustible 1st cycle charge, as a function of first cycle fueling, is produced immediately after enriched cranking fuel injection.

Bench fuel injection experiments were performed to investigate the levels of generated fuel vapor immediately after fuel injection into a closed vessel. A synthetic fuel mixture was used consisting of six individual fuel components that are representative of gasoline. Vessel (e.g. port) temperature and pressure were varied, as well as sample location and sample delay time after injection. Vessel vapor space samples were collected and processed in a gas chromatograph in order to quantify the contribution to the fuel vapor by the various fuel components. Companion modeling was performed in order to evaluate two fuel vapor mixture preparation models (Raoult's Law and NIST's SUPERTRAPP). Results indicate that approximately 1/6 to 1/3 of the injected fuel mass is in the vapor form immediately after fuel injection (as a function of temperature). SUPERTRAPP modeling indicates that the injected fuel mass is approximately in equilibrium with 6% of the available air.